Currently, wide area networks (WANs) are primarily structured for a point-to-point delivery of bandwidth in the form of static ‘pipes’ using TDM e.g. SONET (synchronous optical network)/SDH (synchronous digital hierarchy) and WDM based optical technologies. A SONET signal (i.e. such as STS-48, meaning 48 synchronous transport streams) is typically composed of multiple STS-1's which are assigned to various resources or clients, with the greater the number of STS-1's representing increased bandwidth. Networks based on these technologies enable services, such as traditional private line services, which have the following characteristics:                Point-to-point connectivity with ubiquity of access;        Determinism, whereby bandwidth is 100% dedicated to the connection at all times using time domain multiplexing;        Isolation, whereby individual services have fully dedicated and separated resources;        Static, whereby connections are made on a medium to long time frame basis;        Symmetric, whereby both the outbound and inbound paths have the same bandwidth quanta; and,        Non-dynamic, whereby the bandwidth quanta are constant over the life of the connection.        
Protection mechanisms, for providing alternate transport paths in the event of a failure of a working transport path, are normally achieved within a WAN transport network by providing redundancy for services of fixed bandwidth. These known protection mechanisms include, for SONET, UPSR (a path switched mechanism), BLSR (a line switched mechanism), Linear 1+1, Linear 1:1 and Linear 1:N and, for wavelengths, O-BLSR, O-UPSR, 1+1 wavelength switching and 1+1 line switching. Disadvantageously, however, these known protection mechanisms utilize substantial redundancy. For the BLSR and 1+1 APS line protection mechanisms and the UPSR path protection mechanism twice the network bandwidth is reserved for all service traffic (i.e. to provide the active path and the restoral path). Thus, on using these existing protection mechanisms, service providers are limited to providing either network survivability, at the cost of wasting half of the network bandwidth for protection, or full usage of the network bandwidth at the cost of no protection. The “extra traffic” 1:1 line protection mechanism differs from 1+1 line protection in that the protection bandwidth is made available for use on a “best efforts” basis such that when a network failure occurs, the best effort traffic is dropped to allow the protected traffic access to the available resources. For 1:N line protection a single network path is used as the restoration path for N active channels. Thus, this protection mechanism also uses less than twice the operating bandwidth but the bandwidth needed to provide protection remains undesirably high and, moreover, multiple failures occurring simultaneously may not result in enough bandwidth to allow protection to occur.
More recently, a new class of data service has emerged which relies upon an on-going reallocation of bandwidth (i.e. STS-1's) amongst the clients by means of WAN networking devices within the link layer, examples of such services being high speed GbE, Fibre Channel and HDTV services. This reallocation of bandwidth can be accomplished on an in-service basis, with no perceived interruption in the data communications service by the clients. Although this new service class, which is essentially packet-based, holds some of the same characteristics as the foregoing traditional services and remains well served by 100% deterministic TDM or WDM networks, it has characteristics which are the opposite of traditional services, in particular, flexible bandwidth. This new class of data services is point-to-point in nature, deterministic and isolated, like the foregoing traditional services, but is different in that: (i) it is non-symmetric (ingress and egress traffic are generally unequal); (ii) it is dynamic (connection bandwidth varies over the life of the connection in response to non-static service loads); and, (iii) it is packet-based, such that the application can, in principle, make use of semi-arbitrary transport bandwidths by using flow control mechanisms which guarantee packet delivery or by using higher level protocols which resend any lost packets.
For this new class of data service, there is a need for means to provide different levels of protection for different service paths. In addition, there is a need for a protection switching mechanism that allows full network resource usage during normal operation while at the same time allowing for all services to be protected under failure conditions.